1 Take the rough track from the bottom right corner of the car park, walking downhill towards Compton Abbas. Pass an old chalk quarry and continue downhill. Soon turn right up some wooden steps and cross a stile to access Compton Down. Bear left and uphill towards a fence. Follow a track that contours round, just below the top of the hill, heading towards the saddle between the down and Melbury Hill.

2 Pass a steep, natural amphitheatre on your left, go across the saddle and turn left at the fence. Follow this to the top of Melbury Hill - a steep climb but well worth it for the views. Pass the scar of an ancient cross dyke, on the left as you climb, and look down the other side to the silvery tower of Melbury Abbas church.

3 A trig point marks the top of the hill, with fantastic views all around, including Shaftesbury on its ridge to the north and the ridges of Hambledon Hill to the south east. Retrace your route downhill, with views over Melbury Down and to Compton Abbas Airfield. Turn right on to the farm track. After a short distance bear left, down a steep path, to a gate. Go through this and bear immediately left through a second gate. Go straight along the muddy field edge towards Compton Abbas. Pass through a gate and emerge on to a road.

4 Turn left and follow this road right round a sharp bend. Pass the tower of the original church, isolated in its small graveyard. Continue along the lane, passing houses of varying ages, with the spire of the modern church ahead in the trees. Descend between high hedges and turn left at the junction. Continue on this winding road through the bottom of the village, passing attractive, stone-built, thatched cottages.

5 Pass Clock House and turn left up the bridleway, signposted 'Gore Clump'. The gravel track gives way to a tree-lined lane between the fields. Go through a gate and continue straight on. Cross a stile by a gate and continue ahead along the edge of a field. In the corner, turn left along a fence and walk up the track above some trees to reach a gate. Pass through this on to Fontmell Down. Continue straight ahead on the rising track. After ½ mile (800m) ignore the stile to the right and keep straight ahead along the fence, to reach the top of the hill and a stile into the car park.

Since the end of the Second World War over 80 per cent of the chalk downs in England have been altered or lost because enriching artificial fertilisers have been introduced and land has been claimed for arable crops. Grazing is the key, in a scheme first introduced by the neolithic farmers. Without grazing, the close-cropped grass of the downs would soon revert to scrub and woodland. Modern management is therefore based on restoring the old farming cycles of grazing by sheep and cattle and maintaining the land for the benefit of threatened wildlife as well as for agricultural output. Preservation of the precious habitat of the outstanding area of Melbury and Fontmell Downs is in the hands of the National Trust with assistance from the Dorset Wildlife Trust.

A chief beneficiary of this policy is the butterfly, for more than 35 species have been recorded here. Some have very specific requirements for their survival. The silver spotted skipper, for example, breeds in only 14 places in Britain, and only one in Dorset - Fontmell Down. They lay their eggs on the underside of sheep's fescue grass, but the grass has to be just the right length. If the juicy new grass shoots are nibbled by the sheep in August, the caterpillars will starve. Adonis blues are hardly less demanding - they need a tightly packed, south-facing, warm grassy slope. The grand-sounding Duke of Burgundy fritillary, on the other hand, likes to live on the edge - the edge of the sward, that is, where the cowslips blossom in springtime. (This need for a bit of rough may be a betrayal of its origin as the more humble 'Mr Vernon's small fritillary', for it was renamed in the 18th century.)

The wealth and variety of wild flowers found on these chalky downs is, of course, the other delight. They bloom unmolested, thriving on the poorer soils, not squeezed out by faster-growing monocultures. In summer look for the vivid violet-blue specks of early gentians in the turf, the tiny stalked spikes of the mauve milkwort and the deeper purple of thyme. They give way in autumn to the browny yellow flowers of the carline thistle and the spiralling, white-flowered spikes of autumn lady's tresses.

In autumn, this is a place to find glow-worms. About the length of a fingernail, these little creatures were once a common sight. It is the females who glow. Wingless and defenceless, they hide during the day, but at night crawl on to vegetation to shine their lower abdomens upwards to attract males flying by. The intense green pinpoint of light is caused by oxyluciferin, manufactured by specially adapted body cells which combine oxygen, water and an enzyme to emit light without generating heat.

While you're there

Just east of here, over the border in Wiltshire, Win Green Hill (another National Trust property) is crowned by a ring of trees. It's the highest point of the ancient royal forest of Cranborne Chase, and the views are superb. When he tired of the hunt, King John hung out at nearby Tollard Royal.

What to look for

As you walk towards Compton Abbas, pause at the churchyard of old St Mary's. Rest a moment on the great mounting block by the wall, to admire the ancient farmhouse opposite. All that remains of the old church is the ghostly, pale tower, blocked up and left to the pigeons. In the graveyard itself are some crumbling tombs and the weathered stump of an old cross. A new St Mary's was built within the village in 1866.

Where to eat and drink

Compton Abbas boasts the 17th-century Milestones Tearoom, just south of the church and accessible from the main road. It promises morning coffee, lunches and afternoon teas, and if the weather is sunny you can take it in the patio garden.